1. Field of the Invention
The present invention is generally related to a mounting system for a marine propulsion device and, more particularly, to a support system for a jet pump which both isolates the propulsion device from the marine vessel and prevents water leakage into the marine vessel.
2. Description of the Prior Art
Many different types of marine vessels are well known to those skilled in the art. One particular type of marine propulsion device includes a jet pump that expels water in order to provide thrust for a marine vessel, such as a jet boat or personal watercraft.
U.S. Pat. No. 3,948,206, which issued to Tyler on Apr. 6, 1976, describes a jet powered watercraft. The jet powered watercraft has a motorcyclelike configuration. Longitudinally aligned front and rear skis are located in spaced relation below a hull and operate to hydrodynamically lift the watercraft to a cruise position by relative water flow upon the undersides of the skis. The rear ski and a jet pump are secured as an integral unit to an engine. The rear ski includes an opening through which water passes to the jet pump, and further includes channels on either side of the opening to collect and carry away entrained air. The engine is located in the hull and is cooled by water supplied by the jet pump which it drives. The front ski is rotatable for steering and is resiliently extensible for stability in turning. The center of buoyancy of the watercraft is above its center of gravity so that the craft is self-righting. The exhaust and cooling systems are arranged to eliminate flooding despite location of portions of the engine below water when the craft is at rest. The jet pump discharge nozzle is completely out of the water in the cruise position of the craft for maximum thrust. In FIG. 6 of the Tyler patent, a mounting means is identified by reference numeral 42 which shows an elastomeric member disposed between a portion of the hull and the marine propulsion device.
U.S. Pat. No. 4,193,367, which issued to Benincasa et al on Mar. 18, 1980, described a boat that is designed to withstand the force of underwater explosions. The vessel comprises a hull which consists of a single skin bottom plating comprising a plurality of large area membrane members supported by structural members about their outer periphery only and being of low areal density so as to deflect rapidly and substantially in response to the force of the shock wave of an underwater explosion without permanent deformation and whose personnel and machinery compartments are supported from hull structure members, such as bulkheads, solely by shock absorbing mounts.
U.S. Pat. No. 5,720,638, which issued to Hale on Feb. 24, 1998, discloses an engine drive shaft coupler for a personal watercraft. The jet propelled watercraft has a coupling assembly to couple an engine crankshaft to a jet pump impeller shaft. The coupling assembly can accommodate substantial engine crankshaft vibrations, yet effectively isolates the jet pump impeller from transverse movement. The coupling assembly includes an engine crankshaft coupling head, an intermediate coupler, an impeller shaft coupling head, and two elastomeric isolators positioned between each of the coupling heads and the intermediate coupler. The intermediate coupler is supported exclusively by the elastomeric isolators, and is allowed to tilt transversely to the rotational axis of the intermediate coupler to accommodate engine crankshaft displacement. The coupling assembly is practical for personal watercraft because, although elastomeric isolators wear or shred quickly in the presence of transverse misalignment, elastomeric isolators provide significant durability in the presence of a reasonably amount of angular displacement. The coupling assembly allows the engine to be softly mounted to the hull of the watercraft, and therefore significantly reduces engine noises resonating from the watercraft hull.
U.S. Pat. No. 5,282,444, which issued to Ito et al on Feb. 1, 1994, describes a power transmitting system of a small boat. An improved arrangement for connecting an engine output shaft to a propulsion unit input shaft is described. Also provided is an arrangement for balancing an engine within the craft against undesirable operational forces tending to render the craft unstable. The connecting assembly includes a coupling arrangement utilizing elastomeric vibration dampening members. One of the dampening members possesses a high degree of elasticity, while another of the dampening members possesses a low degree of elasticity. A durable, yet efficient vibration dampening coupling arrangement, which is additionally able to act as a universal joint, is thereby achieved. The engine balancing arrangement includes a flywheel which rotates in response to the crankshaft assembly of the engine. The flywheel is weighted, and rotates in a direction opposite to that of the crankshaft assembly, so that a rotational momentum is achieved by the flywheel to offset undesirable rotational forces created by the crankshaft assembly.
U.S. Pat. No. 5,938,490, which issued to Rodler on Aug. 17, 1999, describes a outboard marine propulsion system for a vessel in which an intake duct having an intake orifice positioned for receiving water is described. The intake duct includes a curved flow path directing walls curved continuously to provide a 180 degree turn for the water so as to direct the water flowing in an initial direction to a direction opposite the initial direction. An annular duct contiguous with the intake duct at the end of the intake duct is positioned opposite the intake orifice. The annular duct has walls curved continuously to provide a second substantially 180 degree turn to direct water flowing therethrough through a continuous change in direction of substantially 180 degrees such that the water is flowing in a direction approximate that of its initial direction of the intake orifice and substantially opposite the direction to which it entered the annular duct.
The patents described above are hereby explicitly incorporated by reference in the description of the present invention.
One problem that occurs when a marine propulsion device, such as a jet pump, is supported by a hull of a watercraft, such as a personal watercraft or a jet boat, is that the support mechanism must generally serve two distinctly different purposes. One purpose is to support the marine propulsion device in such a way that severe vibrations are isolated and inhibited from being transmitted to the hull of the watercraft. Another purpose of the support structure is to prevent water from leaking into the watercraft through an opening provided to facilitate the transfer of torque through the hull from an engine to an impeller. In most applications, these two purposes work in conflict with each other. In other words, in order to effectively prevent leakage of water past the support structure, significant clamping forces are often used to compress a resilient portion of the support structure. However, the compression of a resilient support structure tends to facilitate the transfer of forces through the resilient member and therefore increases the transmission of vibration from the marine propulsion device to the hull of the watercraft. It would therefore be significantly beneficial if a means could be provided to adequately prevent water from leaking through or around the support structure while also providing a sufficiently soft and resilient mounting structure that is effective in isolating vibrations and inhibiting those vibrations from being transmitted from the marine propulsion device to the hull of the watercraft.